The persistence of symptoms in patients treated for Lyme disease remains unexplained. One possible reason could be immune system dysfunction, including antibodies that react against the patient. To study this possibility, these researchers studied whether antibodies targeting endothelial cell growth factor, a normal human protein, were associated with post-treatment Lyme disease syndrome. They found that while antibodies were observed in patients with early and later disease symptoms, they were mostly absent in patients with post-treatment Lyme syndrome.